Evolution by Natural Selection

Life’s Natural History is a Record of Succession & Extinction

Evolution of life has altered the Earth

In historical context Darwin did not originate the idea of evolution!!!

Charles Darwin (1809 – 1882) English naturalist who proposed the theory of evolution by natural selection

HMS Beagle Voyage 1831-1836 Darwin sailed around the world on the HMS Beagle and carefully studied thousands of different plants and animals main mission of the Beagle was to chart South American coastline

The Galapagos Islands Most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. 800 km west of mainland

Unique species

Galapagos Giant Tortiose Galapagos tortoises

Blue-footed Booby Blue-footed booby

Galapagos marine iguanas

The Birds… Galápagos birds One particular group… 22 of the 29 species of birds on the Galapagos are endemic - found only on these islands One particular group… at first, he paid little note to a series of small but distinctive birds some were woodpecker- like, some warbler-like, & some finch-like

Darwin’s finches Darwin was amazed to find out they were all finches 14 species but only one species on mainland of South America - 800 km away all presumably originated from mainland

Correlation of species to food source Adaptive radiation – divergent evolution in which ancestral species evolve into an array of species to fit a number of diverse habitats. Adaptive radiation - divergent evolution in which ancestral species evolve into an array of species to fit a number of diverse habitats.

Darwin’s finches Differences in beaks Darwin’s conclusions associated with eating different foods adaptations to foods available on islands Darwin’s conclusions when original South American finches reached islands, adapted to available food in different environments over many generations, the finches changed anatomically & behaviorally accumulation of favorable traits led to the emergence of different species

Darwin’s finches Finches with beak differences allowed them to… successfully feed successfully compete successfully reproduce pass successful traits onto their offspring

Evolution by Natural Selection Evolution is the gradual change in a species, or populations over time, not individuals. Darwin was the first scientist to realize that evolution can work by natural selection. Natural Selection – Is a mechanism for change in populations. It occurs when organisms with favorable variations survive, reproduce, and pass their variations to the next generation E.g. Thick fur is a favorable trait in cold environments Due to survival of the fittest.

Essence of Darwin’s ideas His theory was simple… Variation exists in natural populations Many more offspring are born each season than can possibly survive to maturity As a result, there is a struggle for existence Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the characteristics of a species Over time, and given a steady input of new variation into a population, these processes lead to the emergence of new species

Natural Selection Darwin referred to all of these factors together as natural selection: Variation production of more offspring than can survive Competition for food, for mates & nesting spots, to escape predators differential survival based on traits

Variation in Populations Evolution by natural selection happens in populations, not individuals. A single organism cannot evolve. Populations evolve. Populations evolve because there is variation Variation causes some organisms to be better fit than others. Better fit organisms are more likely to survive and pass their genes to the next generation

Witness to Evolution Peppered Moth dark vs. light variants

Peppered moth Year % dark % light 1848 5 95 1895 98 2 1995 19 81

Why did the population change? Peppered moth Why did the population change? early 1800s = pre-industrial England low pollution lichen growing on trees = light colored bark late 1800s = industrial England factories = soot coated trees killed lichen = dark colored bark mid 1900s = pollution controls clean air laws return of lichen = light colored bark industrial melanism genetically determined melanism as a population phenomenon especially in moths in which the proportion of dark individuals tends to increase due to differential predation especially by birds which more easily find and eat lighter-colored individuals in habitats darkened by industrial pollution

Evolution by Artificial Selection Artificial Selection: Humans choose individuals with certain traits for breeding After many generations of selection, dramatic evolutionary changes can result Dogs Fruits/Vegetables Livestock

Evidence for Evolution Adaptations Structural Mimicry Camouflage Physiological Fossil Record Comparative Anatomy Homologous Analogous Vestigial Embryological Development DNA Similarities

Evidence #1 - Adaptations All organisms have adaptations which help them survive in their particular environment Adaptation: a structure or behavior that helps an organism better survive in its environment

Adaptations #1 - Structural Evolution of Mole Rats Pressure from predators led them to live underground. Structural adaptations include large teeth and claws to help them survive in their underground environment and defend themselves from predators since they are blind. Vision had no survival advantage for them.

Adaptations #2 - Mimicry Mimicry: a structural adaptation that enables one species to resemble another species E.g. A harmless species might mimic a poisonous one

Adaptations #3 - Camouflage Camouflage: a structural adaptation that allows a species to blend in with its surroundings Camouflage organisms survive to reproduce

Adaptations #4 - Physiological Many bacteria have evolved resistance to antibiotics in the last 50 years Pests have evolved resistance to pesticides Structural adaptations develop over millions of years. Physiological evolves faster because they are changes in organism’s metabolic processes.

Natural selection in action Insecticide & drug resistance insecticide didn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective

Evidence #2 - Fossil Evidence Fossil: Any trace of a dead organism Fossils show the evolution of species over the past millions of years Fossil evidence proves that modern species have evolved from ancient species

Archaeopteryx

Puijila the walking seal

Evolutionary transition from fish to amphibians Tiktaalik

Evidence #3 - Comparative Anatomy Homologous structures: Body structures on different organisms that are similar in structure (same bones) and DID evolve from a common ancestor

Homologous Structures

Comparative Anatomy Analogous structures: Body structures on different organisms that are similar in function but DID NOT evolve from the same ancestor (bird wing and butterfly wing)

Moth (insect) Pterodactyl (reptile) Bat (mammal) Bird Analogous Wing Structures

Comparative Anatomy Vestigial structure: body structure in an organism that no longer serves its original purpose but was useful to an ancestor (useless wings on the African ostrich)

Evidence #4 - Embryological Development Early in development, human embryos and embryos of all other vertebrates are very similar, which suggests that all vertebrates are related Embryo – earliest stage of growth and development of both plants and animals.

Evidence #5 - DNA Similarities Nearly all organisms have DNA, ATP, and many of the same enzymes The DNA (genes) of closely related organisms looks very similar